Process of fabricating refractory metal forms



Nov. 28, 1967 H. H. HALL, JR 3,354,691

PROCESS OF FABRICATING REFRACTORY METAL FORMS Filed NOV. 13, 1964 FIG.2

FIG!

FIG.4

HAROLD H. HALL JR.

INVENTOR.

ATTORNEY United States Patent 3,354,691 PROCESS OF FABRICATING REFRACTORY METAL FORMS Harold H. Hall, Jr., Marblehead, Mass., asslgnor to Sylvania Electric Products Inc., a corporation of Delaware Filed Nov. 13, 1964, Ser. No. 410,980 5 Claims. (Cl. 72-371) ABSTRACT OF THE DISCLOSURE A method of forming refractory metal wire into uniform shapes comprising: Winding the wire on a desired shaped mandrel; removing and measuring the deformation caused by spring 'back of the material; forming a new mandrel with built-in twist to counteract the deformation; thereby wire formed on the new mandrel will compensate for spring-back in the finished metal forms and a finished form will have desired uniform shape.

This invention relates to an improved method of fabricating refractory metal wire forms in a myriad of shapes (other than round or helical) from metals such as tungsten, tantalum, molybdenum or the like.

There are many uses for refractory metal wire forms in industry. One very important application is an endless refractory metal belt used specifically with high temperature furnaces. Refractory metal belts for this particular application are very difficult and costly to fabricate. One possible way to fabricate an endless belt of refractory metal is to wind wire into various continuous shapes wherein the length of the finished shape Wlll constitute the width of the belt. The wire shapes or forms are then interleaved so that a refractory metal rod may be inserted through the staggered turns of the form, thereby securing the individual wire forms together. This procedure will be repeated until an endless belt of wire forms of a desired length is fabricated.

The above example is one of many applications of refractory wire forms or shapes. Another major application is in heating elements used for vacuum and/or inert or reducing atmosphere furnaces of the resistance or electronic type. Such heating elements can be made in a circular shape that will holdwo-rk pieces during the heating operation. These elements can have electrical characteristics substantially identical to those known to the prior art, but yet be structurally far superior to those made from sheets.

With wire having a diameter of 0.005 to 0.250 inch, the fabrication of the refractory metal wire shapes frequently has been a very difiicult if not an impossible task. Previously, the refractory metal wire was wound on a straight, flat mandrel which acts as a core. Subsequently, when the wire form was removed from the mandrel, the wire distorted uncontrollably. In the industry this is referred to as spring-back and it is caused by the mechanical working of the material during winding. This springback prevents uniformity in the formed shapes and is one of the main drawbacks in the fabrication of the formed shapes other than round or helical.

It is necessary in industry to procure refractory metal forms of various shapes, for use in high temperature furnace components. It is therefore necessary to overcome the difficulty of springback. With this in mind, I propose a novel method of producing uniform aligned shapes which eliminate springback in the finished design. Briefly my method involves the following steps: A refractory metal wire is wound on a straight flat mandrel, having the desired width and height characteristics. When wound the wire is then removed from the straight, flat "ice mandrel and the degree of twist or springback of the form is measured. A new mandrel is then made in a special shape to counteract the twist encountered by using a straight mandrel. When a wire is wound on this special mandrel, the springback will be compensated for in the wire shape. Under the same conditions of that of Winding of the straight mandrel, a new refractory metal wire is wound on the new twisted mandrel, which will now produce formed wire shapes of aligned uniformity.

Accordingly, the primary object of my invention is to form refractory metal wire into uniform shapes.

Another object of my invention is to provide a method of producing refractory metal forms with predetermined number of turns per inch.

Other objects, features and advantages will become apparent to those skilled in the art upon reading the following specification when taken in conjunction with the accompanying drawings.

The various figures of the drawings are steps taken for the fabrication of refractory metal forms of aligned uniformity.

FIGURE 1 is an elevational view of refractory metal wire wrapped about a straight mandrel.

FIGURE 2 is a plan view of the refractory metal wire after removal from the straight mandrel showing in particular the springback of the turns of the wire.

FIGURE 3 is an elevational view of a twisted mandrel used in a further step to overcome the distortion of the wire form as seen in FIGURE 2.

FIGURE 4 is an elevational view of the twisted mandrel seen in FIG. 3 with a refractory metal wire wound about said mandrel.

And FIGURE 5 is a top plan view of the finished refractory metal wire form after removal of the form from the twisted mandrel.

The manner of producing aligned uniform refractory metal forms is accomplished by the following procedure.

With the inspection of FIGS. 1-5 it can be appreciated that a stepped procedure is attained to produce a uniform refractory metal form. In FIG. 1 a refractory metal wire is shown wound to a desired number of turns per inch about a straight mandrel. In FIG. 2 the distortion of the wire form is shown after it is removed from the straight mandrel. Thereafter a new mandrel, as seen in FIG. 3 is made to a shape similar to a spiral shape. This new spiral shaped mandrel can be seen in FIG. 4 with a new wire formed thereon with the same number of turns per inch as was the case in FIG. 1. In FIG. 5 a completed wire form is shown after removal from the newly formed spiral mandrel.

For a specific example I use an elongated metal bar 10 as a basic mandrel, the cross section of the mandrel will establish the general contour or shape of the inner diameter of the finished form. The first step in the procedure is as follows: A length of refractory metal wire 12 is preheated and then wound about the mandrel 10 to a desired number of turns per inch.

The degree of heat applied to the wire will depend entirely on the composition size and shape of the wire form to be made. Some refractory metal requires little or no heat before forming, whereas more brittle refractory metal requires a great deal of heat before it becomes ductile enough to be formed. The heat range utilized in working refractory metal of the above perimeters falls into the range of between 800 F.-l50'0 F. Within this range refractory metal wire can be made ductile enough for proper forming.

After the desired amount of turns of wire 12 are wrapped about the straight mandrel 10, to make a desired form 14, the form 14 is removed from mandrel 10. As seen in FIG. 2 after the wire form 14 is removed and is free of the mandrel 10, a definite twist of the wire form 14 takes place. FIG. 2 shows a plan view of the twisted form 14 showing in particular the sp-ringback as it is referred to in the art. The twist or springback can be calculated by many methods but basically the twist is shown at angle A. This twist or springback of the wire form is uniformly spread throughout the length of the form therefore it can be readily assumed that this particular angle or twist can be counteracted by forming the mandrel in an opposite direction of rotation, of the initial wind of the wire 12.

After a new twisted mandrel 16 is made having the desired amount of twist the winding of a new piece of wire 18 about this new mandrel will produce an endless quantity of uniformly aligned refractory metal wire forms 20. It must be noted that in winding of a new wire 18 the same procedure will be followed, that is, pre-heating the wire to the same temperature and winding the exact number of turns per inch as that of the original wire 12 that was formed on the straight mandrel 10.

The wire form 20 is then removed from the twisted mandrel 16 and as viewed in FIG. 5 which is a top plan view of the completed wire form 20, the new Wire form 20 is of a number of aligned turns with no twist whatsoever. A required amount of heat can be applied to the completed form to stress relieve the metal, the amount of heat will depend entirely on the type of metal used in the wire form. An endless amount of wire forms of the identical type of refractory metal can be fabricated on this pretwisted mandrel with the desired results of uniform aligned wire forms.

What I claim is:

1. A method of manufacturing refractory metal wire forms having two oppositely disposed equal short sides and two opposing equal sides that are longer in length than said short sides, the steps which comprise: winding 21 length of refractory metal wire about a substantially straight preliminary mandrel; separating said wire form from said preliminary mandrel and allowing said wire to takea fixed set; forming a spiral mandrel having a shape opposite to the fixed set formed in the winding on said preliminary mandrel, winding 2. length of refractory metal wire about said spiral mandrel, the cross-section of which has two short oppositely disposed sides and two opposing sides that are longer than said short sides, separating said wire from said spiral mandrel and allowing the resulting wire form to spring back into a shape wherein said short sides of each turn and said longer sides of each turn are aligned.

2. A method of manufacturing refractory metal wire forms having at least two regular flat surfaces extending along the length thereof, the steps which comprise: winding a length of refractory metal wire about a substantially straight preliminary mandrel; separating said wire form from said preliminary mandrel and allowing said wire to take a fixed set; forming a spiral mandrel having a shape opposite to the fixed set formed in the winding on said preliminary mandrel, winding a length of refractory metal wire about said spiral mandrel having at least two substantially flat surfaces, said mandrel having a predetermined number of turns per inch, removing said wire from said mandrel and allowing the resulting wire form to spring back into a shape having at least two regular, substantially flat, uniform surfaces; heating the wound wire form to the required temperature to stress relieve the metal.

3. A method of manufacturing refractory metal wire forms having at least two regular flat surfaces extending along the length thereof, the steps which comprise: winding a length of refractory metal wire about a substantially straight preliminary mandrel; separating said wire form from said preliminary mandrel and allowing said wire to take a fixed set; forming a spiral mandrel having a shape opposite to the fixed set formed in the winding on said preliminary mandrel, winding a length of refractory metal wire having a diameter of 0.005 to 0.250 inch about said spiral mandrel having and at least two substantially fiat surfaces, said mandrel having a predetermined number of turns per inch, removing said wire from said mandrel and allowing the resulting wire form to spring back into a shape wherein there are at least two regular, substantially fiat, uniform surfaces thereon.

4. The method according to claim 3 wherein the refractory metal is tungsten.

5. The method of manufacturing refractory metal wire forms having at least two regular flat surfaces extending along the length thereof, the step which comprise: winding a length of refractory metal wire having a diameter of 0.005 to 0.250 inch about a substantially straight preliminary mandrel, separating said wire form from said preliminary mandrel and allowing said wire to take a fixed set; forming a spiral shaped mandrel having a twist opposite to the fixed set found in the winding of said preliminary mandrel, separating said wire form from said twisted mandrel and allowing the resulting form tospring back into a shape wherein there are at least two regular, substantially fiat, uniform surfaces, heating said completed wire form at a temperature to stress relieve said desired shape.

References Cited UNITED STATES PATENTS 397,861 2/1889 Kelly 7237l 1,191,514 7/1916 Jameton 72371 1,668,016 5/1928 Hauschild et a1. 71.5 1,897,412 2/1933 Adams 72-339 2,371,674 3/ 1945 Caminez 72-371 CHARLES W. LANHAM, Primary Examiner, E. M, CQMBS, Assistant Examiner. 

1. A METHOD OF MANUFACTURING REFRACTORY METAL WIRE FORMS HAVING TWO OPPOSITELY DISPOSED EQUAL SHORT SIDES AND TWO OPPOSING EQUAL SIDES THAT ARE LONGER IN LENGTH THAN SAID SHORT SIDES, THE STEPS WHICH COMPRISE: WINDING A LENGTH OF REFRACTORY METAL WIRE ABOUT A SUBSTANTIALLY STRAIGHT PRELIMINARY MANDREL; SEPARATING SAID WIRE FORM FROM SAID PRELIMINARY MANDREL AND ALLOWING SAID WIRE TO TAKE A FIXED SET; FORMING A SPIRAL MANDREL HAVING A SHAPE OPPOSITE TO THE FIXED SET FORMED IN THE WINDING ON SAID PRELIMINARY MANDREL, WINDING A LENGTH OF REFRACTORY METAL WIRE ABOUT SAID SPIRAL MANDREL, THE CROSS-SECTION OF WHICH HAS TWO SHORT OPPOSITELY DISPOSED SIDES AND TWO OPPOSING SIDES THAT ARE LONGER THAN SAID SHORT SIDES, SEPARATING SAID WIRE FROM SAID SPIRAL MANDREL AND ALLOWING THE RESULTING WIRE FORM TO SPRING BACK INTO A SHAPE WHEREIN SAID SHORT SIDES OF EACH TURN AND SAID LONGER SIDES OF EACH TURN ARE ALIGNED. 